Gorantla Sai Manoj N V T, Mondal Kartik Chandra
Department of Chemistry, Indian Institute of Technology Madras, Chennai 600036, India.
ACS Omega. 2021 Jul 6;6(28):17798-17810. doi: 10.1021/acsomega.1c00648. eCollection 2021 Jul 20.
The Donor base ligand-stabilized cyclopentadienyl-carbene compounds L-CH (L = HC, aAAC; (COMe)C, Py; aNHC, NHC, PPh; SNHC; aAAC = acyclic alkyl(amino) carbene, aNHC = acyclic N-hetero cyclic carbene, NHC = cyclic N-hetero cyclic carbene, SNHC = saturated N-hetero cyclic carbene, Py = pyridine) (, , ) have been theoretically investigated by energy decomposition analysis coupled with natural orbitals for chemical valence calculation. Among all these compounds, aNHC=CH () and PhP=CH () had been reported five decades ago. The bonding analysis of compounds with the general formula L=CH () [L = (HC, aAAC, (COMe)C, Py] showed that they possess one electron-sharing σ bond and electron-sharing π bond between L and CH neutral fragments in their triplet states as expected. Interestingly, the bonding scenarios have completely changed for L = aNHC, NHC, PPh, SNHC. The aNHC analogue () prefers to form one electron-sharing σ bond (C-C) and dative π bond (C ← C) between cationic (aNHC) and anionic CH fragments in their doublet states. Similar bonding scenarios have been observed for NHC () and PPh () (P-C, P ← C) analogues. In contrast, the SNHC and CH neutral fragments of SNHC=CH () prefer to form a dative σ bond (C → C) and a dative π bond (C ← C) in their singlet states. The pyridine analogue is quite different from from the bonding and aromaticity point of view. The nucleus-independent chemical shifts of all the abovementioned species (-) corresponding to aromaticity have been computed using the gauge-independent atomic orbital approach.
供体碱配体稳定的环戊二烯基 - 卡宾化合物L - CH（L = HC，无环烷基（氨基）卡宾；(COMe)C，吡啶；无环N - 杂环卡宾，N - 杂环卡宾，三苯基膦；饱和N - 杂环卡宾，Py = 吡啶）（，，）已通过能量分解分析结合化学价计算的自然轨道进行了理论研究。在所有这些化合物中，无环N - 杂环卡宾=CH（）和三苯基膦=CH（）在五十年前就已被报道。通式为L = CH（）[L =（HC，无环烷基（氨基）卡宾，(COMe)C，吡啶]的化合物的键合分析表明，正如预期的那样，它们在三重态下L和CH中性片段之间具有一个电子共享σ键和电子共享π键。有趣的是，对于L =无环N - 杂环卡宾、N - 杂环卡宾、三苯基膦、饱和N - 杂环卡宾，键合情况完全改变。无环N - 杂环卡宾类似物（）在其双重态下倾向于在阳离子（无环N - 杂环卡宾）和阴离子CH片段之间形成一个电子共享σ键（C - C）和配位π键（C←C）。对于N - 杂环卡宾（）和三苯基膦（）（P - C，P←C）类似物也观察到了类似的键合情况。相比之下，饱和N - 杂环卡宾=CH（）的饱和N - 杂环卡宾和CH中性片段在其单重态下倾向于形成一个配位σ键（C→C）和一个配位π键（C←C）。吡啶类似物从键合和芳香性的角度来看与有很大不同。已使用规范无关原子轨道方法计算了上述所有物种（ - ）对应于芳香性的核独立化学位移。
